Pulsed heating system



2 Sheets-Sheet 1 E. J. VANDIVERE ETAL PULSED HEATING SYSTEM INVENTORSfin M0 at MAW/1667853 1 ZZRNEY Se t. 27, 1966 Filed Nov. 8, 1963 p 1965E. J. VANDIVERE ETAL 3,275,802

PULSED HEATING SYSTEM 2 Sheets-Sheet 2 Filed Nov. 8, 1965 s m m w mUnited States Patent 3,275,802 PULSED HEATING SYSTEM Edward J. Vandivereand Lawson M. Phyfe, Santa Fe,

N. Mex., assignors to Reynolds Electrical & Engineering Co., Inc., SantaFe, N. Mex.

Filed Nov. 8, 1963, Ser. No. 322,318 11 Claims. (Cl. 219-499) Thisinvention relates to heating systems. In particular the inventionrelates to a heating system involving the use of a radiating panel and acontrol circuit for intermittently supplying energy to the panel.

It is an object of this invention to provide a heating system wherebythe energy supplied to the panel will be in the form of rapidly repeatedpulses, the duration of the pulses being a function of the temperatureof the panel whereby the panel will be maintained at an average meantemperature which varies through a small temperature range, the meantemperature being a function of the temperature within the space heatedby the panel.

Another object of the invention is to provide a pulsed heating systemwherein the pulsing of the system is entirely independent of thefrequency of the line supplying the energy to the heating system.

Still another object of the invention is to control the repetition rateof pulsing of the panel in accordance with the temperature existingwithin the space heated by the panel.

Other objects and advantages of the invention will be apparent from thefollowing description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a diagram of a system including a circuit in accordance withthe invention;

FIG. 2, a diagram of the system with a heating panel adapted for usetherein; and,

FIG. 3, an enlarged section on the line 3--3 of FIG. 2.

Considering the drawings in greater detail at 10 in FIG. 2 is generallyindicated a heating panel. Insofar as this invention is concerned,various forms of electric heating devices may be employed, said devicesconstituting the load controlled by the circuit. The heater here shownfor illustrative purposes constitutes a panel including an electricallyconductive film 12, such as a binder of conductive particles, of a crosssection and material capable of carrying the heating current. This filmis attached or mounted next to an insulating backing sheet 14 which isattached to or mounted on a protective and heat radiating sheet 16,preferably formed of sturdy material such as steel. The heat radiatingsurface may be mounted in a suitable frame and if desired covered bydecorative paper, not shown. Conductive strips or terminals 18 areprovided to connect the conductive film 12 to an electric source.

The terminals 18 are connected to a controller 28. Also electricallyconnected to the controller is a heat sensitive device 30 mounted inheat sensing relationship to the panel 10, the mounting beingsufficiently close so that the device is sensitive to the temperature ofthe panel rather than the temperaure of the space heated by the panel.Thus, the device 30 may be mounted directly on the panel for better heatconduction therefrom.

Also, if desired, but not necessary to the functioning of the invention,is a second heat sensitive device 32 mounted outside the heated space,this second device also being connected with the controller andfunctioning as will be explained. The controller is furnished with powerfrom a normal A.C. house supply, as by a power cord and plug 33connected to a 240 volt source of supply capable of furnishingkilowatts.

Mounted on the controller is a potentiometer control knob 34 operativeto afford compensation for functioning of components within thecontroller and an operating knob 38 which functions to throw a switchwithin the controller to either a HI position wherein the averagetemperature of the panel is maintained at a high level, or to a LOposition wherein the average temperature of the panel is maintained at alow level.

The circuit within the controller and its associated parts areillustrated in FIG. 1. In said figure the heater is indicated at 12. Theheater is fed with unfiltered fully rectified alternating current fromthe house mains via the line cord and plug 33. Preferably the voltage isthat existing across the outside mains of the house supply, nominally at240 volts and at 60 cycles per second. The current is fed via fuses 36,e.g. 25 ampere fuses, and master switch 38 to a full wave rectifier 40comprised of diodes 42, the heater load 12 being in the output of therectifier. Thus the heater 12 will be fed with a 120 cycle per secondpulsing alternating current. The period or duration of each pulse isunder control of a high current silicon controlled rectifier 44, as a 5kw. electronic switch, in series with the load.

A high current silicon rectifier 46 is also in series with the loadcircuit, this rectifier helping to insure the switching off of thecurrent flow through the rectifier 44 when the pulsing current reachesZero voltage by reason of the voltage developed across rectifier 46,this voltage effectively allowing the gate to be negative with respectto the cathode when no gate signal is present. This permits the use of asilicon controlled rectifier, which exhibits higher than average leakagecurrent, thereby eliminating the need for selection in production units.

The anode of the silicon cont-rolled rectifier while pulsed at the rateof 120 cycles per second permits the passage of current through the load12 only for a portion of the entire period of the pulse as determined bythe pulsed repetitive frequency of the voltage impressed on the gatingelectrode 48.by an oscillator, the frequency of which is variable from 0to more than 10 times line frequency. The circuitry for obtaining thepulsed repetitive frequency will now be described.

A silicon unijunction transistor 50 is proivded with an emitter 52, anelectrode 54 at base 1 terminal of the transistor and an electrode 56 atbase 2 terminal of the transistor. The transistor is part of arelaxation oscillator circuit including a second transistor 60 andprotecting resistor 62 in series with paralleled capacitor 64 andresistor 66, the emitter 52 of the unijunction transistor beingconnected at the junction between the resistor 62 and the paralleledcapacitor and resistor. The unijunction transistor has base 1 terminalconnected to the negative conductor 68 of the rectified direct currentvia a protective resistor 70 while base 2 terminal is connected via aresistor 72 to the positive conductor 74 of the rectified direct currentsource. The resistor 72 renders the transistor 50 more temperaturestable in operation.

The pulsing direct current from the rectifier 40 to the oscillator andother parts of the circuit is filtered by a conventional filtercomprised of series resistors 75, 76 and 78 and shunting capacitors 80and 82. A voltage regulating zener diode 84 shunts the output from thefilter. The transistors and other parts of the circuit are protected bya half ampere fuse 86 and further controlled by a switch 88. Base 1 ofthe unijunction transistor is connected to the gating electrode 48 by aline 90. To prevent spurious pulses from affecting the gating of thesilicon controlled rectifier 44, a resistor 92 is interposed in the lineand a filtering capacitor 94 shunts lines 90 and 68, the resistor andcapacitor forming a differentiating combination.

Variation in the frequency of operation of the oscillator circuit isaccomplished by varying the effective re 3 sistance of the transistor60, that is to say, by varying the potential applied to the base of thetransistor and so varying its current carrying capacity. This basepotential is under control of the switch 96 operated by the knob 38, theoutdoor sensitive device 32 and the panel heat sensitive device 30.

Voltage is applied to the base of the unijunction device as follows:When the switch 96 is in the HI position, as shown in FIG. 1, filtereddirect current flows through the voltage dividing network comprising theoutdoor senser 32, a potentiometer 08 under control of the knob 34, anempirically selected resistor 100 selected to be of a value such thatthe potentiometer 98 would be at center position for a predeterminedroom temperature, a loading resistor 102 and a voltage divider resistor104 to line 68.

The base of an amplifying transistor 106 is connected in betweenresistors 102 and 104 and the voltage on the base is thereforeresponsive to the response of device 32 which preferably is anon-sensitive heat senser having a positive coefficient of resistance.Its sensitivity is much less than that of a thermistor and it istherefore more adaptable to outdoor temperature measurements which mayvary sharply and rapidly. In lieu of the use of the senser indicated,the heat sensing device can be inserted in series with the resistance104, below the junction with the base of the transistor, but the sensingdevice would then have to be a non-linear resistance, such as athermistor having a negative coefficient of resistance.

When the switch 96 is set to the LO position, an extra resistor 108 isplaced in the voltage divider string, thus reducing the voltage at thebase of transistor 106. The transistor is then biased to a lessconductive state, reducing the power delivered to the load, as will bemade clear. The switch 06 provides a given power setback such as mightbe desirable at night or if the enclosed space or room were not to beoccupied for a given time, the value of this setback being determined bythe ratio of the resistance of resistor 108 to the resistance of theremainder of the voltage dividing string.

Also controlling the transistor 106 and connected between the line 74and the emitter of transistor 106 is the panel mounted thermistor 30. Abias generating resistance 110 connects the emitter and the line 68.Resistor 112 provides the means whereby a variable voltage may beestablished at the collector depending on the voltages at the base, asdetermined by the outdoor thermal senser, and at the emitter, asinfluenced by the panel heat thermal senser, and at the emitter, asinfluenced by the panel heat thermal senser. A line 114 connects thejunction between the collector of the transistor 106 and the resistance112 with the base of a second amplifying transistor 116 whose emitter isconnected with line 74 via a resistor 118 and whose collector isconnected via potential establishing resistor 120 to line 68.

A third transistor 122 has its emitter directly connected to line 74 andits collector connected to line 68 via a potential establishing resistor124. The base of transistor 122 is connected via a line 126 to thejunction between the collector of transistor 116 and the resistance 120.

The fourth transistor 60 has its emitter connected to line 74 via aresistor 128 and its collector connected to line 68 via a resistor 62,as heretofore described. The base of transistor 60 is connected via aline 130 to the junction between the collector of transistor 122 and theresistance 124.

The circuit values around transistor 106 are such that thermistor 30vastly overcompensates for temperature changes and in so doing providesthe measure of temperature sensitivity necessary for control.Transistors 116 and 60 are temperature-compensated by the use of thedescribed emitter resistances. This stability is achieved at the expenseof some gain, but this is compensated for by the use of four cascadedtransistors, thereby achieving high heat stability and sensitivity ofthe circuit.

Transistor 122 has no compensating resistor in its emitter circuitbecause its action is opposite to that of transistors 116 and 60, andthe combination of slightly overcompensated transistors 116 and 60 withuncompensated transistor 122, as an intermediate amplifying stage,provides overall compensation without costly selection procedures. Thesilicon unijunction transistor 50 is inherently temperature stable andits stability is further enhanced by the use of the resistor 72 in thebase 2 circuit.

It should be noted that the gated rectifier 44 is turned off each timethe unfiltered pulsing direct current reaches zero. In addition to theresistor 75, a diode 132 is provided which prevents a charge stored infilter capacitor from cutting olf the rectifier 44.

It will be noted that because of the filtered supply to the unijunctiontransistor, its frequency is entirely independent of the line supplyfrequency, and the pulses transmitted to the silicon controlledrectifier in the heater load circuit are independent of the linefrequency. In practice, the frequency of the oscillator may operateanywhere from Zero to more than ten times the frequency of thealternating current source. Thus where a large number of heater unitsare coupled into a single supply system there is very little likelihoodof simultaneous demands of power on the supply line thereby improvingthe wave form characteristics and power factor over a system wherein thepulsing of the silicon controlled rectifier is synchronized with linefrequency.

It will be obvious to one skilled in the art that various changes may bemade in the invention without departing from the spirit and scopethereof and therefore the invention is not limited by that which isillustrated in the drawings and described in the specification, but onlyas indicated in the accompanying claims.

What is claimed is:

1. A heating system comprising lines adapted to be coupled to analternating current source, a rectifier connected to said source toconvert the alternating current to a pulsating direct current, a gatingdevice and a heater in series with said rectifier, said heater having asensing element primarily receiving its heat from said heater, afiltered direct current supply, independent of the frequency of thealternating current source an oscillator connected to said independentdirect current supply, said oscillator being connected to said gatingdevice to control its operation, and means connected to said sensingelement to control the frequency of said oscillator.

2. A heating system comprising a heater, a direct current pulsatingsource feeding said heater, a first means sensitive to the temperatureof said heater to control the repetition rate of the pulses applied tothe heater, and other means of less sensitivity than the first means,sensitive to ambient temperatures uninfluenced by said heater toadditionally control the average temperature of the heater.

3. A heating system as defined in claim 2 wherein said other means has aresistance in series therewith which may be by-passed to vary theaverage temperature which the heater may assume under control of thefirst heat sensitive means.

4. A heating system comprising a heater, a circuit furnishing pulseddirect current to said heater, 3. gating device in series with theheater, an oscillator whose output is connected to the gating device tocontrol its operation, a heat sensitive device influenced mainly byambient temperature connected to the oscillator and controlling thepulse repetition rate of said oscillator, and means controlling saidheat sensitive device to vary the operating point of said heat sensitivedevice.

5. A heating system including a pulsating direct current source, aheater and gate in series with said source, an oscillator operating at afrequency ranging from Zero to more than ten times the frequency of thesource controlling the operation of said gate, and means sensitive totemperature conditions temperature to control the frequency of saidoscillator.

6. A heating system comprising a source of alternating current, a fullwave bridge circuit converting the alternating current into pulseddirect current, a series connected heater, silicon controlled rectifierand silicon rectifier across said bridge circuit, said siliconcontrolled rectifier having a gating electrode, a filtering circuitincluding a shunt capacitor across the output from said bridge circuit,an oscillator connected across the filtered direct current source andconnected to the gating electrode to control the flow of current throughthe heater, means sensitive to temperature changes to control thefrequency of said oscillator, and a filtering resistance-capacitorcombination connected to the gating electrode to prevent spurious pulsesfrom being applied to the gating electrode.

7. A heating system comprising a heater in a pulsed direct currentcircuit, a gating device having a control electrode in series with saidheater, an oscillator connected with the control electrode, a heatsensitive device controlling the frequency of said oscillator and anamplifier interconnecting the heat sensitive device and the oscillatorand comprising three cascaded transistors, a direct current potentialsource for the transistors, the first and third transistors having theemitter connected to the positive source of potential via a resistor andthe intermediate second stage having its emitter directly connected tothe positive potential source.

8. In a heating system, a heater, an oscillator controlling theapplication of current to said heater, a heat sensitive devicecontrolling the frequency of said oscillator, and a transistorizedamplifier between the heat sensitive device and the oscillator, saidamplifier comprising a transistor the base of which is connected to avoltage divider in one leg of which there is a resistor and in the otherleg of which is located said heat sensitive device said second leg alsoincluding a potentiometer to adjust the midpoint of operation of saidheat sensitive device.

9. In a heating system, a heater, an oscillator controlling theapplication of current to said heater, 3. heat sensitive devicecontrolling the frequency of said oscillator, and a transistorizedamplifier between the heat sensitive device and the oscillator, saidamplifier comprising a transistor the base of which is connected to avoltage divider in one leg of which there is a resistor and in the otherleg of which is located said heat sensitive device, there also beingincluded in said other leg a series connected resistance and a switchfor bypassing said resistance, where by to change the potential on thebase of the transistor independently of said heat sensitive devicecontrol.

10. In a heating system, a heater, an oscillator controlling theapplication of current to said heater, a heat sensitive devicecontrolling the frequency of said oscillator, and a source of directcurrent potential, said oscillator comprising a unijunction transistorhaving an emitter and two base electrodes, a resistance connecting eachbase electrode with a respective terminal of the direct current source,a second transistor across the direct current source having a baseelectrode, emitter and collector, means responsive to the heat sensitivedevice for varying the potential of the base electrode, a resistancebetween one terminal of the direct current source and one of the emitterand collector electrodes, the other of the emitter and collectorelectrodes being connected to the emitter of the unijunction transistor,and a paralleled capacitor and resistance connected between the emitterof the unijunction transistor and the other terminal of the directcurrent source.

11. In a heating system as claimed in claim 10, the addition of anotherresistor in the connection from the emitter of the unijunctiontransistor to the other one of emitter and collector electrodes of thesecond transistor.

References Cited by the Examiner UNITED STATES PATENTS 2,840,680 6/1958Mills 219-494 2,981,479 4/1961 Kyle 219-494 3,069,087 12/1962 Thomas219-519 3,107,285 9/1963 Knapp 219-499 3,149,224 9/1964 Horne et al219-501 3,161,759 12/1964 Gambill et al 219-501 RICHARD M. WOOD, PrimaryExaminer.

L. H. BENDER, Assistant Examiner.

2. A HEATING SYSTEM COMPRISING A HEATER, A DIRECT CURRENT PULSATINGSOURCE FEEDING SAID HEATER, A FIRST MEANS SENSITIVE TO THE TEMPERATUREOF SAID HEATER TO CONTROL THE REPETITION RATE OF THE PULSES APPLIED TOTHE HEATER, AND OTHER MEANS OF LESS SENSITIVITY THAN THE FIRST MEANS,SENSITIVE TO AMBIENT TEMPERATURES UNINFLUENCED BY SAID HEATER TOADDITIONALLY CONTROL THE AVERAGE TEMPERATURE OF THE HEATER.